Using a metal-containing layer as an etching stop layer and to pattern source/drain regions of a finfet

ABSTRACT

A fin structure of a FinFET device is formed over a substrate. A first layer is formed over the fin structure. A gate layer is formed over the fin structure and over the first layer. The gate layer is patterned into a gate stack that wraps around the fin structure. A second layer is formed over the first layer and over the gate stack. A first etching process is performed to remove portions of the second layer formed over the fin structure, the first layer serves as an etching-stop layer during the first etching process. A second etching process is performed to remove portions of the first layer to expose a portion of the fin structure. A removal of the portions of the first layer does not substantially affect the second layer. A source/drain region is epitaxially grown on the exposed portion of the fin structure.

PRIORITY DATA

The present application is a utility application of provisional U.S.Application No. 62/552,554, filed on Aug. 31, 2017 and entitled “Using ametal-containing layer as an etching stop layer and to patternsource/drain regions of a FinFET”, the content of which is herebyincorporated by reference in its entirety.

BACKGROUND

The semiconductor industry has progressed into nanometer technologyprocess nodes in pursuit of higher device density, higher performance,and lower costs. As this progression takes place, challenges from bothfabrication and design issues have resulted in the development ofthree-dimensional designs, such as fin-like field effect transistor(FinFET) device. A typical FinFET device is fabricated with a thin “fin”(or fin-like structure) extending from a substrate. The fin usuallyincludes silicon and forms the body of the transistor device. Thechannel of the transistor is formed in this vertical fin. A gate isprovided over (e.g., wrapping around) the fin. This type of gate allowsgreater control of the channel. Other advantages of FinFET devicesinclude reduced short channel effect and higher current flow.

However, conventional FinFET devices may still have certainshortcomings. One shortcoming is that the manner in which thesource/drain regions are defined for conventional FinFET fabrication hasnot been optimized. For example, the FinFET device may suffer fromepi-selectivity loss in the formation of source/drain regions.

Therefore, while existing FinFET devices and the fabrication thereofhave been generally adequate for their intended purposes, they have notbeen entirely satisfactory in every aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is best understood from the following detaileddescription when read with the accompanying figures. It is emphasizedthat, in accordance with the standard practice in the industry, variousfeatures are not drawn to scale and are used for illustration purposesonly. In fact, the dimensions of the various features may be arbitrarilyincreased or reduced for clarity of discussion.

FIG. 1 is a perspective view of an example FinFET device.

FIGS. 2A-12A are Y-cut cross-sectional side views of FinFET devices atvarious stages of fabrication according to embodiments of the presentdisclosure.

FIGS. 5B-8B and 10B-12B are X-cut cross-sectional side views of FinFETdevices at various stages of fabrication according to embodiments of thepresent disclosure.

FIG. 4D is a top view of FinFET devices at a stage of fabricationaccording to embodiments of the present disclosure.

FIGS. 5C, 7C, 8C, and 11C are perspective three-dimensional views ofFinFET devices at different stages of fabrication according toembodiments of the present disclosure.

FIGS. 7D, 8D, and 11D-12D are magnified Y-cut cross-sectional side viewsof a portion of the FinFET devices at different stages of fabricationaccording to embodiments of the present disclosure.

FIG. 13C is a perspective three-dimensional view of FinFET devices at astage of fabrication according to embodiments of the present disclosure.

FIG. 14 is a flow chart illustrating a method of fabricating a FinFETdevice in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

It is understood that the following disclosure provides many differentembodiments, or examples, for implementing different features of theinvention. Specific examples of components and arrangements aredescribed below to simplify the present disclosure. These are, ofcourse, merely examples and are not intended to be limiting. Forexample, the formation of a first feature over or on a second feature inthe description that follows may include embodiments in which the firstand second features are formed in direct contact, and may also includeembodiments in which additional features may be formed between the firstand second features, such that the first and second features may not bein direct contact. In addition, the present disclosure may repeatreference numerals and/or letters in the various examples. Thisrepetition is for the sake of simplicity and clarity and does not initself dictate a relationship between the various embodiments and/orconfigurations discussed. Moreover, various features may be arbitrarilydrawn in different scales for the sake of simplicity and clarity.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. For example, if the device in the figures is turned over,elements described as being “below” or “beneath” other elements orfeatures would then be oriented “above” the other elements or features.Thus, the exemplary term “below” can encompass both an orientation ofabove and below. The apparatus may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein may likewise be interpreted accordingly.

The present disclosure is directed to, but not otherwise limited to, afin-like field-effect transistor (FinFET) device. The FinFET device, forexample, may be a complementary metal-oxide-semiconductor (CMOS) deviceincluding a P-type metal-oxide-semiconductor (PMOS) FinFET device and anN-type metal-oxide-semiconductor (NMOS) FinFET device. The followingdisclosure will continue with one or more FinFET examples to illustratevarious embodiments of the present invention. It is understood, however,that the application should not be limited to a particular type ofdevice, except as specifically claimed.

The use of FinFET devices has been gaining popularity in thesemiconductor industry. Referring to FIG. 1, a perspective view of anexample FinFET device 50 is illustrated. The FinFET device 50 is anon-planar multi-gate transistor that is built over a substrate (such asa bulk substrate). A thin silicon-containing “fin-like” structure(hereinafter referred to as a “fin”) forms the body of the FinFET device50. The fin extends along an X-direction shown in FIG. 1. The fin has afin width W_(fin) measured along a Y-direction that is orthogonal to theX-direction. A gate 60 of the FinFET device 50 wraps around this fin,for example around the top surface and the opposing sidewall surfaces ofthe fin. Thus, a portion of the gate 60 is located over the fin in aZ-direction that is orthogonal to both the X-direction and theY-direction.

L_(G) denotes a length (or width, depending on the perspective) of thegate 60 measured in the X-direction. The gate 60 may include a gateelectrode component 60A and a gate dielectric component 60B. The gatedielectric 60B has a thickness t_(ox) measured in the Y-direction. Aportion of the gate 60 is located over a dielectric isolation structuresuch as shallow trench isolation (STI). A source 70 and a drain 80 ofthe FinFET device 50 are formed in extensions of the fin on oppositesides of the gate 60. A portion of the fin being wrapped around by thegate 60 serves as a channel of the FinFET device 50. The effectivechannel length of the FinFET device 50 is determined by the dimensionsof the fin.

FinFET devices offer several advantages over traditional Metal-OxideSemiconductor Field Effect Transistor (MOSFET) devices (also referred toas planar transistor devices). These advantages may include better chiparea efficiency, improved carrier mobility, and fabrication processingthat is compatible with the fabrication processing of planar devices.FinFET devices are also compatible with a high-k metal gate (HKMG)process flow. Thus, FinFET devices may be implemented as HKMG deviceswhere the gates each that have a high-k gate dielectric and a metal gateelectrode. For these benefits discussed above, it may be desirable todesign an integrated circuit (IC) chip using FinFET devices for aportion of, or the entire IC chip.

However, traditional FinFET fabrication methods may still haveshortcomings. One shortcoming is that the manner in which thesource/drain regions are defined for conventional FinFET fabrication hasnot been optimized. As a result, the FinFET device may suffer fromepi-selectivity loss in the formation of source/drain regions. Toimprove the problems associated with conventional FinFET devices, thepresent disclosure utilizes a metal-containing layer in patterningprocesses to help define the source/drain regions of the FinFET devices,as discussed in more detail below. In more detail, FIGS. 2A-12A areY-cut cross-sectional side views of FinFET devices 100 at various stagesof fabrication, FIGS. 5B-8B and 10B-12B are X-cut cross-sectional sideviews of FinFET devices 100 at various stages of fabrication, FIG. 4D isa top view of FinFET devices 100 at a stage of fabrication, FIGS. 5C,7C, 8C, and 11C-13C are perspective three-dimensional views of FinFETdevices 100 at different stages of fabrication, and FIGS. 7D, 8D, and11D-12D are magnified Y-cut cross-sectional side views of a portion ofthe FinFET devices at different stages of fabrication.

Referring now to FIG. 2A, FinFET devices 100 include a semiconductorlayer 110 that is formed over a substrate. In an embodiment, thesemiconductor layer 110 includes a crystal silicon material, such assilicon or silicon germanium. An implantation process may be performedto implant a plurality of dopant ions to the semiconductor layer 110.The dopant ions may include an n-type material in some embodiments, forexample arsenic (As) or phosphorous (P), or they may include a p-typematerial in some other embodiments, for example boron (B), depending onwhether an n-type FET (NFET or NMOS) or a p-type FET (PFET or PMOS) isneeded. For example, Nwells 120A may be formed for the PFET, and Pwells120B may be formed for the NFET.

A plurality of fin structures is formed by patterning the semiconductorlayer 110 through one or more lithography processes. For example, finstructures 150A are formed for the PFET, and fin structures 150B areformed for the NFET. The lithography processes used to form the finstructures 150A/150B may include forming a patterned photoresist, usingthe patterned photoresist to pattern hard mask layers therebelow, andusing the patterned hard mask layers to define the fin structures150A/150B. It is understood that the portions of the fin structures150A/150B may serve as the source, drain, or channel regions of theFinFET devices 100. The channel regions may include silicon or silicongermanium.

Isolation structures 160 are formed to electrically isolate the finstructures 150A/150B. The isolation structures 160 may also be referredto as shallow trench isolation (STI) structures. In some embodiments,the isolation structures 160 contain a dielectric material such assilicon oxide or silicon nitride. The isolation structures 160 may beformed by depositing the dielectric material to fill the openingsdefined by the fin structures 150A/150B, and then performing a polishingprocess (such as chemical mechanical polishing) to planarize the surfaceof the deposited dielectric material. One or more etching processes maythen be performed to the dielectric material to form recesses 170 byremoving portions (but not all) of the material from the isolationstructures 160. The etching processes define the “height” (in theZ-direction of FIG. 1) of the fin structures 150A/150B.

As shown in FIG. 2A, the fin structures 150A/150B protrude upwards(e.g., upward along the Z-axis of FIG. 1) and out of the isolationstructures 160. In other words, at least a portion of each fin structure150A/150B is exposed and not covered by the isolation structures 160. Itis also understood that an optional undoped semiconductor layer (e.g.,undoped silicon) 180 may be disposed between the fin structures 150A andthe N-well in some embodiments. In other embodiments, the layer 180 maybe omitted.

Referring now to FIG. 3A, a layer 200 is formed over the side and topsurfaces of the fin structures 150A/150B for both the PFET and the NFET.The layer 200 is also formed over an upper surface of the isolationstructures 160 and partially fills the recesses 170. The layer 200serves as an etching-stop layer in a later etching process, which willbe discussed below in more detail. Conventional FinFET fabricationprocesses do not form this layer 200.

In some embodiments, the layer 200 includes a dielectric layer, forexample a metal-containing dielectric layer. The presence of metal inthe layer 200 helps facilitate a removal of the layer 200 in a wetetching process to be performed later, where an SC1 solution(H2O:H2O2:NH4OH) and/or an SC2 solution (HCl:H2O2:H2O) may be used as anetchant. In some embodiments, phosphoric acid (H3PO4) may also be usedas an etchant in the wet etching process. The easy removal of the layer200 in the subsequent etching process makes the layer 200 a goodcandidate for being a patterning layer. In some embodiments, the layer200 includes aluminum oxide (Al₂O₃). The layer 200 may be formed to anysuitable thickness using any suitable deposition technique (e.g., CVD,HDP-CVD, ALD, etc.). In the illustrated embodiment, the layer 200 isformed using a conformal CVD and/or ALD deposition process and is formedto have a thickness 205. In some embodiments, the thickness 205 is in arange from about 2 nanometers (nm) to about 20 nm. It is understood thatthe material composition and the thickness range of the layer 200 arespecifically configured so that it can adequately serve as theetching-stop layer and also to facilitate the easy removal in the wetetching process below.

Referring now to FIG. 4A, a gate electrode layer 220 is formed over thefin structures 150A/150B and over the layer 200. In some embodiments,the gate electrode layer 220 is a dummy gate electrode layer that willbe removed in a later process. For example, the gate electrode layer 220may include polysilicon, which will be removed and replaced with a metalgate electrode in a gate-replacement process in a later fabricationstep. The gate electrode layer 220 may be formed by one or moredeposition processes, such as chemical vapor deposition (CVD), physicalvapor deposition (PVD), atomic layer deposition (ALD), or combinationsthereof.

After the deposition of the gate electrode layer 220, one or moreetching processes may be performed to the gate electrode layer 220 todefine a gate length Lg (measured in the X-direction as shown in FIG.1). In other words, the gate electrode layer 220 is patterned by the oneor more etching processes into separate gate electrode stacks 220. Thisis illustrated in more detail in FIG. 4D, which is a top view of theFinFET devices 100. As shown in the top view of FIG. 4D, a plurality offin structures (e.g., the fin structures 150A/150B) extend in theX-direction (the same X-direction as shown in FIG. 1), and a pluralityof patterned gate electrode stacks 220 extend in the Y-direction (thesame Y-direction as shown in FIG. 1). A Y-cut (in the Y-direction) ofthe FinFET devices 100 in the top view produces the cross-sectional viewshown in FIG. 4A. An X-cut (in the X-direction) of the FinFET devices100 in the top view will produce a different cross-sectional view, whichwill be discussed below in more detail with reference to FIGS. 5B-8B and10B-12B.

Referring now to FIGS. 5A, 5B, and 5C, a dielectric layer 230 is formedover the layer 200 and also over the patterned gate electrode stacks220. FIG. 5A is a cross-sectional view obtained using the Y-cut, andFIG. 5B is a cross-sectional view obtained using the X-cut. The X-cutand Y-cut are also illustrated in FIG. 5C, which is a perspectivethree-dimensional view of the FinFET devices 100.

As shown in FIG. 5C (and also in FIG. 5A obtained according to theY-cut), the layer 200 is formed on the side surfaces and top surfaces ofeach of the fin structures 150A and 150B. The dielectric layer 230 isthen formed on the side surfaces and top surfaces of the layer 200. Notethat in FIG. 5A, since the Y-cut is taken outside the gate electrodestacks 220, the gate electrode stacks 220 should not be directly visiblein the cross-sectional view of FIG. 5A. However, to facilitate theunderstanding of the present disclosure, one of the gate electrodestacks 220 is still shown with broken lines in FIG. 5A, to illustratethat it is located “behind” the fin structures 150A/150B and the layers200 and 230.

As shown in FIG. 5C (and also in FIG. 5B obtained according to theX-cut), no portion of the layer 200 is formed on the sidewalls of thegate electrode stacks 220, since the gate electrode stacks 220 areformed and defined after the deposition of the layer 200. But thedielectric layer 230 is formed after the formation of the gate electrodestacks 220, and thus the dielectric layer 230 is formed on the sidewallsof the gate electrode stacks 220. Note that as shown in FIGS. 5A and 5C,there may be one or more hard mask layers 250 disposed over each gateelectrode stack 220. The one or more hard mask layers 250 are used topattern the gate electrode stacks 220 and define the dimensions of thegate electrode stacks 220. In some embodiments, the one or more hardmask layers 250 include an oxide material, for example silicon oxide. Asshown in FIGS. 5B and 5C, the dielectric layer 230 is formed over theside surfaces and top surfaces of the hard mask layers 250.

It is understood that the material compositions of the dielectric layer230 and the layer 200 are configured such that an etching selectivityexists between the dielectric layer 230 and the layer 200 in asubsequent etching process. In other words, the dielectric layer 230 andthe layer 200 have substantially different etching rates (e.g., 10 timesor more) in the subsequent etching process. In some embodiments, thedielectric layer 230 includes a nitride material, for example siliconnitride, while the layer 200 includes a metal-containing oxide material,such as aluminum oxide (Al₂O₃). The dielectric layer 230 is used todefine the active regions and source/drain regions of the FinFET devices100. The dielectric layer 230 also serves as a dummy spacer.

Also note that the X-cut taken to obtain FIG. 5B is taken outside of thefin structures 150A/150B, and thus the fin structures 150A/150B are notvisible in the cross-sectional view of FIG. 5B, and instead theisolation structure 160 is shown as being located below the gateelectrode stack 220. It is understood that if the X-cut is moved to apoint where it intersects with one of the fin structures 150A or 150B(as is the case for some of the figures discussed below), then the finstructure 150A or 150B would be shown as being located below the gateelectrode stack 220, since each gate electrode stack 220 wraps aroundthe top and side surfaces of the fin structures 150A and 150B.

Referring now to FIGS. 6A and 6B, an etching process 300 is performed tothe FinFET devices 100 to remove portions of the dielectric layer 230formed over the fin structures 150A and 150B, while not removingportions of the dielectric layer 230 formed on the sidewalls of the gateelectrode stacks 220. Note that the etching process 300 also removes theportions of the dielectric layer 230 above the hard mask 250, as shownin FIG. 6B. In some embodiments, the etching process 300 includes a dryetching process, which facilitates the selective removal (i.e., removingthe dielectric layer 230 for the fin structures 150A/150B while keepingthe dielectric layer 230 for the gate electrode stacks 220) of thedielectric layer 230. Again, since the X-cut corresponding to FIG. 6B istaken outside of the fin structures 150A/150B, the removal of thedielectric layer 230 over the fin structures 150A and 150B may not bedirectly apparent in FIG. 6B.

As discussed above, the material compositions of the dielectric layer230 and the layer 200 are configured such that an etching selectivityexists between them in the etching process 300. As such, the layer 200functions as an etching-stop layer during the etching process 300. Thatis, the etching process 300 removes the portions of the dielectric layer230 located over the top and side surfaces of the fin structures150A/150B, but the layer 200 prevents the etching process 300 frometching the fin structures 150A/150B themselves.

Referring now to FIGS. 7A, 7B, and 7C, the source/drain regions aredefined for the PFET. Similar to FIG. 5C discussed above, FIG. 7C is aperspective three-dimensional view of the FinFET devices 100, FIG. 7A isa cross-sectional view obtained using the Y-cut, and FIG. 7B is across-sectional view obtained using the X-cut. The Y-cut correspondingto FIG. 7A is taken at the fin structures, as was the case for FIG. 5A.However, the X-cut corresponding to FIG. 7B is now moved (compared toFIG. 5B) such that the X-cut now intersects with the fin structures 150Aof the PFET. As such, FIG. 7B produced by the X-cut in FIG. 7C now showsa portion of the silicon germanium (SiGe) channel 310, which is aportion of the fin structure 150A. Also as shown in FIG. 7B, Nwells 120Aare located below the SiGe channel 310.

In order to define the source/drain regions for the PFET, the NFETportion of the FinFET devices 100 is covered up by a patternedphotoresist layer 330. The PFET portion of the FinFET devices 100 isexposed. An etching process 350 is then performed to the PFET portion ofthe FinFET devices 100. In some embodiments, the etching process 350includes a wet etching process. The etching process 350 removes thelayer 200 but leaves the dielectric layer 230 intact, due to the etchingselectivity between the layer 200 and the dielectric layer 230. Notethat as shown in FIG. 7C, the previous etching process 300 has alreadyremoved the portions of the dielectric layer 230 formed over the finstructures 150A/150B, but portions of the dielectric layer 230 stillremain on the sidewalls of the gate electrode stacks 220. Therefore, theetching process 350 leaves intact the portions of the dielectric layer230 disposed on the sidewalls of the gate electrode stacks 220, whileremoving the layer 200.

In some embodiments, the etching process 350 uses an SC1 solution(H2O:H2O2:NH4OH) and/or an SC2 solution (HCl:H2O2:H2O) as an etchant. Insome other embodiments, phosphoric acid (H3PO4) may also be used as anetchant in the etching process 350. The material composition for thelayer 200 is configured such that it is easily removable by the etchingprocess 350. For example, in embodiments where the layer 200 containsaluminum oxide, aluminum oxide is easily removable by the SC1 solutionand/or the SC2 solution, or by the phosphoric acid. The easyremovability of the layer 200 makes it a suitable layer for performingpatterning processes.

As shown in FIG. 7A, the removal of the layer 200 for the PFET exposesthe top and side surfaces of the fin structures 150A. It is understoodthat in actual fabrication, the removal of the layer 200 may not be100%. In other words, residue of the layer 200 may still remain evenafter the etching process 350 is performed. For example, while the topsurface and the upper parts of the sidewalls of the fin structures 150Amay be exposed after the etching process 350 is performed to remove thelayer 200, the lower parts of the fin structures 150A may still haveremnants of the layer 200 disposed thereon, for example as shown in FIG.7D, which is a more magnified cross-sectional view of the PFET of FIG.7A. As shown in FIG. 7D, while an upper portion of the fin structures150A are exposed, remnants of the layer 200 may still be disposed onsidewalls of a lower portion of the fin structures 150A, even after theetching process 350 is performed.

Similarly, the removal of the dielectric layer 230 in the precedingetching process 300 also may not completely remove the dielectric layer230. For example, as shown in FIG. 7D, residue of the dielectric layer230 may also remain disposed on the remnants of the layer 200 after theetching process 350 is performed. In any case, the exposed portions(i.e., the upper portion) of the fin structures 150A are capable ofepitaxially growing the source/drain regions of the PFET, which will bediscussed below.

Meanwhile, the fin structures 150B for the NFET are not exposed, sincethe layer 200 (which is not removed due to being protected by thepatterned photoresist layer 330) is still disposed on the fin structures150B. In this manner, the removal of the dielectric layer 200 for thePFET (but not for the NFET) exposes the fin structures for the PFET,thereby allowing the S/D regions of the PFET to be defined.

Referring now to FIGS. 8A, 8B, 8C, and 8D, the patterned photoresistlayer 330 is removed, and an epitaxial growth process 370 is performedto epitaxially grow source/drain regions 380 of the PFET. Similar toFIGS. 7A-7D, FIG. 8C is a perspective three-dimensional view of theFinFET devices 100, FIG. 8A is a cross-sectional view obtained using theY-cut, and FIG. 8B is a cross-sectional view obtained using the X-cut,and FIG. 8D is a more magnified cross-sectional view of the PFET of FIG.8A.

As shown in FIGS. 8A-8D, the source/drain regions 380 are grown on theexposed portions (e.g., the upper portions) of the fin structures 150Aduring the process 370. The source/drain regions 380 protrude upwards inthe Z-direction and laterally in the Y-direction. In embodiments wherethe fin structures 150A comprise SiGe, the source/drain regions 380 forthe PFET also comprise SiGe. As shown in FIG. 8D, remnants of the layers200 and 230 may still remain formed on sidewalls of the lower portion ofthe fin structures 150A, and portions of the source/drain regions 380are formed above the remnants of the layers 200 and 230.

Since the NFET portion of the FinFET devices 100 is still covered by thelayer 200, no source/drain regions are formed for the NFET yet. In otherwords, the epitaxial growth process 370 does not grow anything on thefin structures 150B for the NFET, since the fin structures 150B arestill covered by the layers 200 and 230. In certain conventionalschemes, the source/drain regions for the PFET and NFET are grown at thesame time, and as such the SiGe-containing source/drain may be grown forthe NFET, and/or a Si-containing source/drain may be grown for the PFET.This is undesirable and may be referred to as epi-selectivity loss. Incomparison, the layer 200 herein allows the source/drain regions for thePFET to be formed separately from the source/drain regions for the NFET.Consequently, the source/drain regions 380 formed for the PFET compriseSiGe but will be substantially free of Si, and the source/drain regionsformed for the NFET (in a subsequent process discussed below) willcomprise Si but will be substantially free of SiGe. As such, theprocesses of the present disclosure provide epi-selectivity lossimmunity.

Referring now to FIG. 9A, the layer 200 is removed for the NFET. In someembodiments, the removal of the layer 200 may be performed using anetching process 390 that is similar to the etching process 350. Asdiscussed above, since there is etching selectivity between the layer200 and the dielectric layer 230, the removal of the layer 200 byetching does not substantially remove the dielectric layer 230. Afterthe removal of the layer 200, the fin structures 150B are exposed. Onereason for removing the layer 200 here is for process control stability.It helps stabilize process control to remove the layer 200 and thenredeposit the layer (as will be done with reference to FIGS. 10A-10Bdiscussed below) for the next round of patterning.

Referring now to FIGS. 10A and 10B, a layer 400 is formed over the sideand top surfaces of the fin structures 150B for the NFET and over theside and top surfaces of the source/drain regions 380 for the PFET. Thelayer 400 is also formed over an upper surface of the isolationstructures 160. In some embodiments, the formation of the layer 400involves a conformal deposition process. In some embodiments, the layer400 and the layer 200 have the same material composition. For example,the layer 400 may also include a dielectric layer, for example ametal-containing dielectric layer. In some embodiments, the layer 400includes aluminum oxide (Al₂O₃). It is understood that the layer 400will serve substantially the same functionalities as the layer 200discussed above. In other words, it may be said that the formation ofthe layer 400 is equivalent to re-depositing the layer 200.

Note that FIG. 10B is obtained by taking the X-cut at two differentportions of the FinFET devices 100. The PFET shown in FIG. 10B isobtained by taking the X-cut across one of the fin structures 150A, andthe NFET shown in FIG. 10B is obtained by taking the X-cut across one ofthe fin structures 150B. The NFET shown in FIG. 10B illustrates asilicon channel 410 for the NFET, where the silicon channel is a portionof the fin structure 150B for the NFET. Pwells 120B are located belowthe silicon channel 410.

Referring now to FIGS. 11A, 11B, 11C, and 11D, the source/drain regionsare defined for the NFET. FIG. 11C is a perspective three-dimensionalview of the FinFET devices 100, FIG. 11A is a cross-sectional viewobtained using the Y-cut, FIG. 11B is a cross-sectional view obtainedusing the X-cut at two different sections of the FinFET devices 100 (oneX-cut at the PFET and another X-cut at the NFET). FIG. 11D is a moremagnified cross-sectional view of the NFET of FIG. 11A.

The source/drain definition for the NFET is similar to the source/draindefinition for the PFET (except the NFET and the PFET are switched)discussed above with reference to FIGS. 7A-7D. For example, as a part ofthe NFET source/drain definition, the PFET portion of the FinFET devices100 may be covered up by a patterned photoresist layer (not specificallyillustrated herein for reasons of simplicity). The NFET portion of theFinFET devices 100 is then exposed. An etching process similar to theetching process 300 discussed above is performed to the NFET portion ofthe FinFET devices 100 to remove portions of the dielectric layer 230formed over the fin structures 150B. The layer 400 serves as anetching-stop layer during this etching process. Thereafter, an etchingprocess similar to the etching process 350 discussed above is performedto remove portions of the layer 400 for the NFET but leaves thedielectric layer 230 intact, due to the etching selectivity between thelayer 400 and the dielectric layer 230. The removal of the layer 400exposes portions of the fin structures 150B for the NFET. Meanwhile, thesource/drain regions 380 for the PFET are not exposed, since the layer400 (which are not removed due to being protected by the patternedphotoresist layer) is still disposed on the source/drain regions 380 forthe PFET.

A recess etching process 450 is then performed to the FinFET devices 100to etch recesses 460 in the NFET. As is shown in FIGS. 11B-11C, therecesses 460 are formed in the fin structures 150B, for example byetching away portions of the fin structures 150B. Thus, the recesses 460are formed next to the silicon channel 410 of the NFET. FIGS. 11C and11D also show portions of the layer 400 that still remain after theetching of the layer 400. These remaining portions of the layer 400effectively further extend the recesses 460 upwards in the Z-direction.

Due to the Y-cut being taken at the recesses 460, the recesses 460 arenot immediately or apparently visible in FIG. 11A, since the recesses460 correspond to an absence of the fin structures 150B. To facilitatethe understanding of the present disclosure, however, dashed lines areillustrated above the remaining segments of the fin structures 150B inFIG. 11A to represent the recesses 460 (i.e., the portions of the finstructures 150B that have been removed for the NFET).

Referring now to FIGS. 12A, 12B, 12C, and 12D, an epitaxial growthprocess 470 is performed to epitaxially grow source/drain regions 480 ofthe NFET. The layer 400 is removed thereafter. Specifically, FIG. 12C isa perspective three-dimensional view of the FinFET devices 100, FIG. 12Ais a cross-sectional view obtained using the Y-cut, and FIG. 12B is across-sectional view obtained using the one X-cut for the PFET andanother X-cut for the NFET, and FIG. 12D is a more magnifiedcross-sectional view of the NFET of FIG. 12A.

As shown in FIGS. 12A, 12C, and 12D, the source/drain regions 480 forthe NFET are grown on the exposed portions of the fin structures 150Bduring the epitaxial growth process 470. The source/drain regions 480fill the recesses 460 and protrude upwards out of the recesses 460 inthe Z-direction and laterally in the Y-direction. In embodiments wherethe fin structures 150B comprise Si, the source/drain regions 480 alsocomprise Si. As discussed above, the PFET source/drain regions 380 hadalready been formed before the formation of the NFET source/drainregions 480. The separate formation of the PFET and NFET source/drainregion—which is made possible by the unique process flow of the presentdisclosure—allows for higher quality epi-growth of the source/drainregions of the FinFET devices 100. Also as shown in FIG. 12D, since theremoval of the layers 400 and 230 may not be 100%, remnants of thelayers 400 and 230 may remain formed below the source/drain regions 480.The layers 400 and 230 may also be disposed on the sidewalls of thelower portions of the source/drain regions 480.

Note that in the stage of fabrication shown in FIG. 12C, the dielectriclayers 230 (but not the layers 400) are still disposed on the sidewallsof the gate electrode stacks 220. These dielectric layers 230 will beremoved in a subsequent process, and a low-k dielectric material will bedeposited as the sidewall spacer for the gate electrode stacks 220. Inaddition, since the removal of the layers 200, 400, 230 may not be 100%,there may be residual portions of the layers 200, 400 and/or thedielectric layer 230 underneath the epitaxially-grown source/drainregions 380 and 480, for example as shown in FIG. 12C. Note that in someembodiments (such as in the embodiment shown in FIGS. 12A-12D), one ofthe NFET and PFET (e.g., NFET) comprises a recessed fin, while the otherone of the NFET and PFET (e.g., PFET) comprises a non-recessed fin, overwhich a source/drain may be formed.

A plurality of other processes is performed to complete the fabricationof the FinFET devices 100. For example, a gate replacement process maybe performed to replace the gate electrode stacks 220—which are dummygate electrode stacks—with metal gate electrode stacks. For example, asa part of the gate replacement process, an interlayer dielectric (ILD)is formed over the isolation structures 160. The ILD may contain siliconoxide. A polishing process such as chemical-mechanical-polishing (CMP)is performed to planarize the upper surface of the ILD. The dummy gateelectrode stacks 220 are then removed, and a metal gate electrode stackmay be formed in place of each removed dummy gate electrode stack. Insome embodiments, the metal gate electrode stack may include a workfunction metal component and a fill metal component. The work functionalmetal component is configured to tune a work function of itscorresponding FinFET to achieve a desired threshold voltage Vt. Invarious embodiments, the work function metal component may contain:TiAl, TiAlN, TaCN, TiN, WN, or W, or combinations thereof. The fillmetal component is configured to serve as the main conductive portion ofthe gate electrode. In various embodiments, the fill metal component maycontain Aluminum (Al), Tungsten (W), Copper (Cu), or combinationsthereof. It is also understood that a high-k gate dielectric may beformed beneath each metal gate electrode stack. A high-k dielectricmaterial is a material having a dielectric constant that is greater thana dielectric constant of SiO2, which is approximately 4. In anembodiment, the high-k gate dielectric includes hafnium oxide (HfO2),which has a dielectric constant that is in a range from approximately 18to approximately 40. In alternative embodiments, the high-k gatedielectric may include ZrO2, Y203, La2O5, Gd2O5, TiO2, Ta2O5, HfErO,HfLaO, HfYO, HfGdO, HfAlO, HfZrO, HfTiO, HfTaO, or SrTiO.

Referring now to FIG. 13C, a diagrammatic three-dimensional view of theFinFET devices 100 is illustrated after the gate replacement processdiscussed above has been performed. As shown in FIG. 13C, a gate stack600 is formed to replace the dummy gate electrode stack 220. The gatestack 600 may include a high-k gate dielectric and a metal gateelectrode as discussed above. An ILD 610 is formed on the sidewalls ofthe gate stack 600. The gate stack 600 and the ILD are formed over theisolation structure 160. The portion of the FinFET devices 100 shown inFIG. 13C is an NFET, and thus fin structures 150B and epitaxially-grownsource/drain regions 480 are formed.

As discussed above, due to process window limitations, some residue ofthe layers 400 and 230 may still remain formed on the sidewalls of alower portion of the source/drain region 480 (and below an upper portionof the source/drain region 480). Similarly, some residue of the layers200 and 230 may remain formed on the sidewalls of a lower portion of thefin structures 150A for a PFET (such as illustrated in FIGS. 8D and12D), but the PFET is not illustrated in FIG. 13C for reasons ofsimplicity.

It is understood that the presence of the layers 230 and 200/400 at thisstage of fabrication (i.e., after the gate replacement) is notintentional, nor do these layers serve important functions at thispoint, since the residue of these layers is mostly attributed to processimperfections. Nevertheless, the presence of these layers 230 and200/400 at this stage of fabrication is evidence that the unique processflows discussed above have been performed. In other words, if the finalFinFET device from a given manufacturer is found to contain remnants ofthe layers 230 and 200/400 in the locations discussed above withreference to FIGS. 8D, 12C-12D and 13C, it is likely that the finalFinFET device was fabricated using the unique process flows of thepresent disclosure.

FIG. 14 is a flowchart of a method 800 for fabricating a FinFET devicein accordance with various aspects of the present disclosure. The method800 includes a step 810 of forming a fin structure of a FinFET deviceover a substrate.

The method 800 includes a step 820 of forming a first layer over the finstructure. In some embodiments, the forming the first layer comprisesforming a metal-containing layer as the first layer. In someembodiments, the forming the metal-containing layer comprises forming analuminum-oxide (Al₂O₃) layer with thickness between about 1 nm and about10 nm and is deposited by a conformal CVD and/or ALD process as thefirst layer.

The method 800 includes a step 830 of forming a gate layer over the finstructure and over the first layer.

The method 800 includes a step 840 of patterning the gate layer into agate stack that wraps around the fin structure.

The method 800 includes a step 850 of forming a second layer over thefirst layer and over the gate stack. In some embodiments, the formingthe second layer comprises forming a layer that contains silicon nitrideas the second layer.

The method 800 includes a step 860 of performing a first etching processto remove portions of the second layer formed over the fin structure. Afirst etching selectivity exists between the first layer and the secondlayer in the first etching process, such that the first layer serves asan etching-stop layer during the first etching process. In someembodiments, the first etching process comprises a dry etching process.

The method 800 includes a step 870 performing a second etching processto remove portions of the first layer to expose a portion of the finstructure. A second etching selectivity exists between the first layerand the second layer in the second etching process, such that a removalof the portions of the first layer does not substantially affect thesecond layer. In some embodiments, the second etching process comprisesa wet etching process.

The method 800 includes a step 880 of epitaxially growing a source/drainregion on the exposed portion of the fin structure.

In some embodiments, the second etching process does not completelyremove the first layer but still leaves remnants of the first layer onsidewalls of the fin structure. In some embodiments, the first etchingprocess does not completely remove the second layer but still leavesremnants of the second layer on sidewalls of the first layer.

It is understood that additional process steps may be performed before,during, or after the steps 810-880 discussed above to complete thefabrication of the semiconductor device. For example, the gate stack maycomprise a dummy gate electrode, and the method 800 may further includea step of: replacing the dummy gate electrode with a metal gateelectrode. In addition, the steps 860-880 are performed for a PFET ofthe FinFET device in some embodiments, in which case the method 800 mayfurther repeat the steps 860-880 for an NFET of the FinFET device. Asanother example, the method 800 may include a step of removing the firstlayer and re-depositing the first layer after the source/drain region ofthe NFET has been epitaxially grown but before the repeating. Otherprocess steps are not discussed herein for reasons of simplicity.

Based on the above discussions, it can be seen that the presentdisclosure offers advantages over conventional FinFET and thefabrication thereof. It is understood, however, that other embodimentsmay offer additional advantages, and not all advantages are necessarilydisclosed herein, and that no particular advantage is required for allembodiments. One advantage is that the formation of the metal-containinglayer (e.g., an aluminum oxide layer) allows it to serve as an etchingstop layer for the dielectric layer (e.g., a silicon nitride layer)formed thereover, due to the good etching selectivity between these twolayers. Another advantage is that the metal-containing layer can beeasily removed in a wet etching process, which makes it suitable forpatterning. Yet another advantage is that the unique process flowsdiscussed can reduce epi-selectivity loss during the formation of thesource/drain regions of the PFET and the NFET. Yet another advantage ofthe present disclosure is that the unique fabrication steps discussedherein are easy to implement and are compatible with existingfabrication process flow. Therefore, implementing the present disclosuredoes not lead to increased costs.

One aspect of the present disclosure involves a method of fabricating asemiconductor device. A fin structure of a FinFET device is formed overa substrate. A first layer is formed over the fin structure. A gatelayer is formed over the fin structure and over the first layer. Thegate layer is patterned into a gate stack that wraps around the finstructure. A second layer is formed over the first layer and over thegate stack. A first etching process is performed to remove portions ofthe second layer formed over the fin structure. A first etchingselectivity exists between the first layer and the second layer in thefirst etching process, such that the first layer serves as anetching-stop layer during the first etching process. A second etchingprocess is performed to remove portions of the first layer to expose aportion of the fin structure. A second etching selectivity existsbetween the first layer and the second layer in the second etchingprocess, such that a removal of the portions of the first layer does notsubstantially affect the second layer. A source/drain region isepitaxially grown on the exposed portion of the fin structure.

Another aspect of the present disclosure involves a semiconductordevice. The semiconductor device includes a fin structure that protrudesout of a substrate. A source/drain region is disposed on a sidewall ofan upper portion of the fin structure. A metal-containing material isdisposed on a sidewall of a lower portion of the fin structure.

Yet another aspect of the present disclosure involves a semiconductordevice. The semiconductor device includes a fin structure that protrudesout of a substrate. An upper portion of the fin structure includes arecess. A source/drain region is disposed over the fin structure. Thesource/drain region fills the recess. A metal-containing material isdisposed on a sidewall of a lower portion of the source/drain region.The metal-containing material is disposed below an upper portion of thesource/drain region.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.

Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method, comprising: forming a fin structure ofa FinFET device over a substrate; forming a first layer over the finstructure; forming a gate layer over the fin structure and over thefirst layer; patterning the gate layer into a gate stack that wrapsaround the fin structure; forming a second layer over the first layerand over the gate stack; performing a first etching process to removeportions of the second layer formed over the fin structure, wherein afirst etching selectivity exists between the first layer and the secondlayer in the first etching process, such that the first layer serves asan etching-stop layer during the first etching process; performing asecond etching process to remove portions of the first layer to expose aportion of the fin structure, wherein a second etching selectivityexists between the first layer and the second layer in the secondetching process, such that a removal of the portions of the first layerdoes not substantially affect the second layer; and epitaxially growinga source/drain region on the exposed portion of the fin structure. 2.The method of claim 1, wherein the performing the first etching process,the performing the second etching process, and the epitaxially growingthe source/drain region are performed for a PFET of the FinFET device,and wherein the method further comprises: repeating the performing thefirst etching process, the performing the second etching process, andthe epitaxially growing the source/drain region for an NFET of theFinFET device.
 3. The method of claim 2, further comprising: removingthe first layer and re-depositing the first layer after the source/drainregion of the NFET has been epitaxially grown but before the repeating.4. The method of claim 1, wherein the forming the first layer comprisesforming a metal-containing layer as the first layer.
 5. The method ofclaim 4, wherein the forming the metal-containing layer comprisesforming an aluminum-oxide (Al₂O₃) layer as the first layer.
 6. Themethod of claim 1, wherein the forming the second layer comprisesforming a layer that contains silicon nitride as the second layer. 7.The method of claim 1, wherein the first etching process comprises a dryetching process.
 8. The method of claim 1, wherein the second etchingprocess comprises a wet etching process.
 9. The method of claim 1,wherein: the second etching process does not completely remove the firstlayer but still leaves remnants of the first layer on sidewalls of thefin structure; and the first etching process does not completely removethe second layer but still leaves remnants of the second layer onsidewalls of the first layer.
 10. The method of claim 1, wherein thegate stack comprises a dummy gate electrode, and wherein the methodfurther comprises: replacing the dummy gate electrode with a metal gateelectrode.
 11. A semiconductor device, comprising: a fin structure thatprotrudes out of a substrate; a source/drain region disposed on asidewall of an upper portion of the fin structure; and ametal-containing material disposed on a sidewall of a lower portion ofthe fin structure.
 12. The semiconductor device of claim 11, wherein themetal-containing material comprises aluminum oxide.
 13. Thesemiconductor device of claim 11, further comprising: a nitride materialdisposed on the metal-containing material.
 14. The semiconductor deviceof claim 11, wherein the source/drain region is a source/drain region ofa P-type FinFET.
 15. The semiconductor device of claim 14, wherein thefin structure and the source/drain region each include silicongermanium.
 16. A semiconductor device, comprising: a fin structure thatprotrudes out of a substrate, wherein an upper portion of the finstructure includes a recess; a source/drain region disposed over the finstructure, wherein the source/drain region fills the recess; and ametal-containing material disposed on a sidewall of a lower portion ofthe source/drain region, and wherein the metal-containing material isdisposed below an upper portion of the source/drain region.
 17. Thesemiconductor device of claim 16, wherein the metal-containing materialcomprises aluminum oxide.
 18. The semiconductor device of claim 16,further comprising: a nitride material disposed on the metal-containingmaterial.
 19. The semiconductor device of claim 16, wherein thesource/drain region is a source/drain region of an N-type FinFET. 20.The semiconductor device of claim 19, wherein the fin structure and thesource/drain region each include silicon.